World oil demand growth could fall short of forecasts in 2013, producer group Opec said on Tuesday, citing economic risks in the euro zone and the US.

The Organization of the Petroleum Exporting Countries in a monthly report left its forecast unchanged for now, still expecting that global oil consumption will expand by 840,000 barrels per day (bpd) this year.

"However, there are a number of downward risks to this growth," the report from Opec's Vienna headquarters said. "The euro's instability could lead to even deeper recession in some Mediterranean countries.

"And the potential impact of a full budget cut in the United States could drag down the world economy, consequently reducing oil demand." – Reuters